1. Field of the Invention
The present invention relates to a motor drive unit with a heat sink that cools a power device.
2. Description of the Related Art
Many motor drive unites include a heat sink with a plurality of fins and an air blower such as a fan motor in order to cool electronic components such as a power device (see Japanese Patent Application Laid-Open No. 2005-321287). FIG. 5A and FIG. 5B are perspective views of the appearance of a motor drive unit 17 according to a conventional technique. FIG. 6A and FIG. 6B are schematic diagrams of an internal configuration of the motor drive unit 17 according to the conventional technique. The motor drive unit includes a housing with a housing component 1, a housing component 2, and a housing component 3.
The motor drive unit is installed in a factory or the like so as to be mounted in an electric cabinet for a machine tool or the like. In an environment in the factory around the electric cabinet with the motor drive unit mounted therein, mist of cutting fluid or dust may float. When the electric cabinet is insufficiently closed, outside air containing mist of cutting fluid may infiltrate into the electric cabinet and further into the motor drive unit and adhere to electronic components to make the electronic components defective. In particular, when a fan motor is installed in order to cool the electronic components of the motor drive unit, the electronic components are likely to be defective.
Much mist of cutting fluid or the like may adhere to, for example, areas with a heat sink or the like where cooling air flows concentrically, resulting in droplets of the fluid. The droplets may fall concentrically onto electronic components near the heat sink to make the electronic components defective.
As a conventional measure against the droplets, the electronic components are disposed away from the heat sink and the like to which the droplets are likely to adhere, so as to be prevented from becoming defective as a result of falling droplets. However, the measure may disadvantageously limit the arrangement of the electronic components, making examination of the electronic component arrangement during a design phase difficult and leading to an increased size of a printed circuit board and thus of the motor drive unit. Furthermore, the electronic components disposed away from the heat sink may make patterns longer than necessary and become susceptible to noise. As a result, the electronic components may become defective.